The present invention relates to a semiconductor laser device which finds applications in optical information processing, optical measurement, optical communication or the like.
A prior art semiconductor laser device will be explained with the help of a cross-sectional view thereof as shown in FIG. 21.
The device includes a heat sink 2 fixed on a side of an element mounting base 1 and a semiconductor laser chip 3 (referred to as "laser chip" hereafter) mounted on heat sink 2. The light radiating surface of the laser chip 3, the upper side of the heat sink 2 and the upper surface of the element mounting base 1 are made flush with one another, and at the same time a laser output light detecting photodiode 4 is placed at a lower position opposite to the light radiating surface of the laser chip 3 and also a signal detecting photodiode 5 is placed on the upper side of the element mounting base 1.
Next, operation of the device having the foregoing structure will be explained.
The radiating light 6 sent from the laser chip 3 towards the upper direction of FIG. 21 is reflected by an object and inputted to the signal detecting photodiode 5 as reflected light 7 for signal processing. On the other hand, the laser light sent out from the surface opposite to the light radiating surface of the laser chip 3 is inputted to the laser output light detecting photodiode 4 and converted to electric current signals corresponding to the intensity of the laser light. The electric current signals are fedback to a laser chip driving circuit for controlling the output of the laser light in a stabilized manner.
With the foregoing prior art structure, the required assembly work can not be performed efficiently and the position alignment accuracy may be a problem because the laser chip 3 is desirably mounted within a vertical plane while the signal detecting photodiode 5 is mounted horizontally and the laser output light detecting photodiode 4 is mounted within an almost horizontal plane on the element mounting base 1, respectively.
A structure intended for solving the foregoing problem is employed in a semiconductor laser device, of which a cross-sectional view is shown in FIG. 22.
The structure has a V-shaped groove formed on a silicon substrate of (100) lattice plane, both the slanting surfaces of which are formed of (111) lattice plane. One of the slanting surfaces of the groove serves as a reflecting mirror surface 9 whereby radiating laser light is reflected. The main surface of the silicon substrate 8 which joins the other slanting surface is made lower than the other main surface of the silicon substrate 8, and a laser chip 3 is mounted on the lower main surface of the silicon substrate 8 with its front end surface, where the laser light from the laser chip is radiated, disposed in parallel with the ridge where the lowered main surface of the silicon substrate and the slanting surface of the V-shaped groove meet each other.
With the foregoing structure, the laser light radiated horizontally from the laser chip 3 is reflected at the reflecting mirror surface 9 and can be taken out in an almost vertical direction. Accordingly, a signal detecting photodiode (not shown in FIG. 22) and a laser output detecting photodiode (not shown in FIG. 22) can be formed on the main surface of the silicon substrate 8 with high accuracy by means of photolithography.
However, when a V-shaped groove is formed on a silicon substrate 8 of (100) lattice plane with slanting surfaces of (111) lattice plane, there has been a problem that the slanting angle .theta. between the reflecting mirror surface 9 and the surface of the silicon substrate 8 is about 54.degree., causing the center axis of the radiating laser light to tilt from the direction perpendicular to the main surface of the silicon substrate by about 18.degree..
The inventors presently believe the reason why the reflecting mirror surface 9 inherently makes an angle about 54.degree. with the surface of the silicon substrate 8 is because the silicon substrate used here is not cut out with an off-angle of 4.degree. to 14.degree. about an axis of &lt;110&gt; direction as disclosed by the present invention.